Level control in continuous casting

ABSTRACT

Continuous casting of metal, particularly upward pressure casting of metal, in which molten metal is passed from a melting vessel to a mould from which the solidified metal is continuously extracted, wherein pressure changes in the molten metal at a predetermined position within the vessel are detected and the pressure of the molten metal at the inlet to the mould is thereby controlled so as to be substantially constant. The molten metal pressure is preferably controlled by controlling the flow of pressurising gas to the vessel.

United StatesPatent [1 1 Bosworth et a1.

[ Oct. 36, 1973 LEVEL CONTROL IN CONTINUOUS CASTING [75] Inventors: Clive James Arthur Bosworth, Kettering; William Richardson Duguid, Corby, both of England [73] Assignee: British Steel Corporation, London,

England [22] Filed: June 18, 1971 [21] Appl. No.: 154,319

[30] Foreign Application Priority Data June 24, 1970 Great Britain 30,546/70 [52] 11.8. CI. 164/155 [51] Int. Cl B22d 17/32 [58] Field 01 Search 164/119, 155, 154, 164/306, 308

[56] References Cited UNITED STATES PATENTS 3,287,773 11/1966 Woodburn 164/155 X 3,499,580 3/1970 Smith 164/306 X 3,425,483 2/1969 Dearth.... 164/155 3,459,254 8/1969 Dearth.... 164/119 3,412,899 11/1968 Sutter..... 164/155 UX 2,990,592 7/1961 Hursen 164/155 Primary ExaminerJ. Spencer Overholser Assistant ExaminerJohn E. Roethel Att0rney -Nolte and Nolte [5 7] ABSTRACT Continuous casting of metal, particularly upward pressure casting of metal, in which molten metal is passed from a melting vessel to a mould from which the solidified metal is continuously extracted, wherein pressure changes in the molten metal at a predetermined position'within the vessel are detected and the pressure of the molten metal at the inlet to the mould is thereby controlled so as to be substantially constant. The molten metal pressure is preferably controlled by controlling the flow of pressurising gas to the vessel.

3 Claims, 1 Drawing Figure PATENTEDUCT 30 ms 3; 768,542

mawzw LEVEL CONTROL IN CONTINUOUS CASTING This invention is concerned with the continuous casting of metal.

Apparatus has been proposed for the continuous casting of metal articles, e.g. bars or tubes, in which molten metal in a pressure vessel is forced by gas pressure, coupled with the pressure head of the metal itself, into a mould in which the metal solidifies, the solidified metal being continuously extracted from the mould, e.g. by extraction rollers. The general direction of flow from the pressure vessel to the mould is often upwardly. As solidified metal is extracted from the mould, the molten metal level in the pressure vessel, and hence the pressure head of the metal will fall, as also will the rate of flow of molten metal into the mould (or the molten metal level in the mould in the case of upward casting), unless the pressure within the pressure vessel is increased or more molten metal is introduced into the pressure vessel. It is an object of the present invention to overcome or at least substantially reduce this problem.

According to one aspect of the invention there is provided apparatus for the continuous casting of metal comprising a vessel for containing molten metal, a mould having an inlet communicating with the interior of the vessel for receiving molten metal from the vessel, means for continuously extracting solidified metal from the mould, pressure sensitive means disposed at least partly in the vessel and arranged to detect pressure changes at a predetermined position within the molten metal therein, and control means governed by the pressure-sensitive means for maintaining substantially constant the molten metal pressure at the inlet to the mould.

According to another aspect of the invention there is provided a method of continuously casting metal comprising melting the metal in a vessel, passing the molten metal to a mould, continuously extracting solidified metal from the mould, detecting pressure changes at a predetermined position within the molten metal within the vessel, and maintaining substantially constant the molten metal pressure at the inlet to the mould in dependance on' the detection of said pressure changes.

The pressure sensitive means may be arranged to detect pressure changes within the molten metal at a predetermined position which is fixed relative to the mould inlet.

The means for continuously extracting solidified metal from the mould may be adapted to extract the metal in an upward direction, preferably in a tubular form. I

The vessel for containing molten metal may be a pressure vessel, in which case means are included for providing super atmospheric pressure within the pressure vessel.

The means for providing super-atmospheric pressure within the vessel may include means for supplying gas at super atmospheric pressure thereto,

The mould may be located above the pressure vessel such that in operation molten metal is forced upwardly into the mould by the super-atmospheric pressure within the pressure vessel, the control means serving to maintain the level of molten metal in the mould substantially constant.

The control means may comprise means for adjusting the gas pressure in the pressure vessel. In another arrangement, the control means may comprise means for introducing more molten metal into the pressure vessel. In yet another arrangement, the control means may comprise means for changing the positions of the mould and pressure vessel relative to each other vertically, but the mechanical complications would normally render this arrangement unattractive.

The pressure-sensitive device preferably comprises a tube arranged to dip below the surface of the molten metal in the vessel, means for passing gas through the tube into the molten metal and means responsive to changes in the pressure of the gas passing through the tube. The responsive means may comprise a differential pressure measuring instrument having one inlet connected to the tube and another inlet connected through a pressure-control valve to a source of gas under pressure.

A further differential pressure measuring instrument may be connected between the interior of the pressure vessel and the tube to respond to changes in the pressure difference between the vessel and the tube. This further instrument may be arranged to indicate said pressure difference and thereby the molten metal level in the pressure vessel and/or to control an exhaust valve for the pressure vessel.

The following is a description, by way of example, of an embodiment of the invention, reference being made to the accompanying schematic drawing of the apparatus.

The continuous casting apparatus shown inthe drawing comprises a pressure vessel 1 supplied with air or inert gas under super-atmospheric pressure through a solenoid-operated valve 2 and an inlet 3. A ladle 5 containing molten metal 6 is disposed in the vessel 1 and a tubular refractory nozzle 7 is mounted in'sealed relationship to and depending from the top of the vessel 1 into the molten metal 6. A tubular water-cooled mould 8 is mounted on top of the nozzle 7. In use, the pressure .of the gas in the vessel 1 forces molten metal up the nozzle 7 into the mould 8, the metal solidifies at a level S in the mould and the solified metal is continuously extracted upwards by extraction means, part of which is shown diagrammatically at 25.

A dip tube 10 extends down into the molten metal in the ladle 5 to a level which will be referred to as the datum. Conveniently, the lower end of the nozzle 7 also lies on this datum. A gas, preferably an inert gas, e.g. argon, is passed through a reducing valve 11 and a constant flow and pressure device 12 to the tube 10 at a pressure sufficient to keep gas flowing through the open lower end of the tube 10 into the molten metal when maximum pressure exists in the pressure vessel during casting. A differential pressure measuring instrument 14 has one inlet connected to the tube 10 and another (low pressure) inlet connected to a source of air or gas under pressure-through a fine adjustment reducing valve 15. The instrument 14,has an output 16 passed through the tube 10 into the molten metal. The pressure measured by the instrument 14 is proportional to the head of molten metal above the datum and to the specific gravity of the molten metal. The differential pressure at the instrument 14 is now backed off to zero by the application of gas pressure to the low pressure inlet of the instrument, so as to limit the required working range of the instrument and the pressure controller and thereby enhance their accuracy.

The vertical distance between the datum and required molten metal level S in the mould is calculated and the necessary pressure value for gas to be introduced into the pressure vessel is set on the pressure controller 18. The solenoid valve 2 is then opened so that pressurized gas flows into the pressure vessel under the control of the diaphragm valve 21 in conjunction with the pressure controller 18 until the vessel pressure reaches the set value, when molten metal will have risen up the nozzle 7 into the mould 8 as high as the level S. Solidified metal is withdrawn continuously upwards from the mould. As the solidified metal is withdrawn the level of the molten metal 6 in the ladle falls, causing a decrease in the pressure in the tube 10. This decrease is sensed by the instrument 14 which transmits a signal to the pressure controller 18, which adjusts the diaphragm valve 21 to increase the gas pressure in the vessel 1 to maintain the molten metal level at level S in the mould.

A second differential pressure measuring instrument 23 is connected between the pressure vessel 1 and the tube and indicates the difference in pressure between them and therefore the level of metal in the ladle 5. The instrument 23 has an output signal which is fed to a switch or relay 24 which controls the operation of an exhaust valve 17 on the pressure vessel 1. If the pressure in the dip tube 10 falls suddenly due to breakage of the tube or during casting the metal level in the ladle has slowly fallen to a minimum safe working level with a resulting change in the aforesaid pressure difference, the arrangement causes the gas in the pressure vessel to exhaust to atmosphere, so that the apparatus fails safe".

The apparatus may also be used to measure the specific gravity of a liquid. For this purpose, the differential pressure measuring instrument 14 is used to indicate the pressure at the bottom of the dip tube 10. The distance from the bottom of the dip tube to the surface of the liquid in the ladle is measured. As this distance is varied so will the pressure at the bottom of the dip tube vary. The gas pressure above the liquid in the ladle is kept constant, e.g. at atmospheric pressure. The specific gravity is determined by dividing the pressure difference between two depths of immersion of the lower end of the dip tube by the difference-in depth. For example, if a one inch variation in dip tube depth produces a seven inch water gauge pressure change then the specific gravity would be 7.0. Similarly, a two inch variation in dip tube depth producing a 14 inch water gauge pressure change indicates a specific gravity of 7.0.

While various commercially-available control units may be used in the apparatus shown in the drawing, examples of suitable units are as follows. The constant flow and pressure device may be a pneumerstat," Type H.187, manufactured by Williams & James (Engineers) Limited of Gloucester, British Patent No. 696592. The differential pressure measuring instruments may be Differential Pressure Transmitters, Type 212TD, manufactured by Taylor Instrument Companies (Europe) Limited, providing a 3-15 p.s.i. output signal proportional to differential head, and giving local indication of the head in inches water gauge. The range of the differential pressure instrument is determined by the physical dimensions of the vessel and mould and the maximum density of the material to be cast, i.e. the maximum head to be generated. (Taylor Specification Sheet 9841 3Sl-E refers.) The pressure controller may be a Deviation Indicating Controller, Type 544RFll8l0, also made by Taylor (Taylor Specification Sheet 98540 -Sl-E refers.)

We claim:

1. Apparatus for the continuous casting of metal comprising a pressure vessel for containing molten metal; means for providing super-atmospheric pressure within the pressure vessel; a mold having an inlet communicating with the interior of the vessel for receiving molten metal from the vessel; means for continuously extracting solidified metal from the mold; pressure sensitive means including a tube arranged to dip below the surface of the molten metal to a predetermined level in the pressure vessel; means for passing gas through the tube into the molten metal; and control means including a differential pressure measuring instrument having an inlet connected to the tube and another inlet connected through a pressure control valve to a source of gas under pressure; the differential pressure measuring instrument having an output connected to a pressure controller arranged to control the flow of pressurizing gas into the pressure vessel whereby the molten-metal pressure at the inlet to the mold is maintained substantially constant and including a further differential pressure measuring instrument connected between the inte rior of the pressure vessel and the tube to respond to changes in the pressure difference between the vessel and the tube.

2. Apparatus according to claim 1 wherein the mould is located above the pressure vessel such that in opera tion molten metal is forced upwardly into the mould by the super-atmospheric pressure within the pressure vessel, the control means serving to maintain the level of molten metal in the mould substantially constant.

3. Apparatus according to claim 1 wherein the means for continuously extracting solidified metal from the mould is adapted to extract the metal in tubular form. 

1. Apparatus for the continuous casting of metal comprising a pressure vessel for containing molten metal; means for providing super-atmospheric pressure within the pressure vessel; a mold having an inlet communicating with the interior of the vessel for receiving molten metal from the vessel; means for continuously extracting solidified metal from the mold; pressure sensitive means including a tube arranged to dip below the surface of the molten metal to a predetermined level in the pressure vessel; means for passing gas through the tube into the molten metal; and control means including a differential pressure measuring instrument having an inlet connected to the tube and another inlet connected through a pressure control valve to a source of gas under pressure; the differential pressure measuring instrument having an output connected to a pressure controller arranged to control the flow of pressurizing gas into the pressure vessel whereby the molten-metal pressure at the inlet to the mold is maintained substantially constant and including a further differential pressure measuring instrument connected between the interior of the pressure vessel and the tube to respond to changes in the pressure difference between the vessel and the tube.
 2. Apparatus according to claim 1 wherein the mould is located above the pressure vessel such that in operation molten metal is forced upwardly into the mould by the super-atmospheric pressure within the pressure vessel, the control means serving to maintain the level of molten metal in the mould substantially constant.
 3. Apparatus according to claim 1 wherein the means for continuously extracting solidified metal from the mould is adapted to extract the metal in tubular form. 